Comment by bigyabai | Hacker News Reader

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Comment by bigyabai | Hacker News Reader

My kingdom for a documented disk image format.

I'll take your kingdom!

ISO 9660.

https://www.iso.org/iso-9660-images-for-computer-files.html

VMDK

https://en.wikipedia.org/wiki/VMDK

Amiga

https://en.wikipedia.org/wiki/Amiga_Disk_File

UDF

https://en.wikipedia.org/wiki/Universal_Disk_Format

Apple Disk Image

https://en.wikipedia.org/wiki/Apple_Disk_Image

VMDK isn't documented there, and is a container for multiple partially documented - and some only reverse engineered - subformats.

Not on wikipedia, but VMDK is part of the DTMF OVF[1] format and thus I believe the .vmdk format would be implicitly made available therein

However, words are words but software is better:

- https://github.com/vmware/open-vmdk#specifications is Apache 2

- the link they cited is bitrotten but Internet Archive has you: https://web.archive.org/web/20210411181842/https://www.vmwar...

1: https://www.dmtf.org/standards/ovf

Unfortunately, no. OVA and OVF are defined in the OVF spec, but VMDK is not.

So congrats on finding the spec for it, as its no longer maintained! Its also no longer followed, either, unfortunately.

VHDX https://learn.microsoft.com/en-us/openspecs/windows_protocol...

About the only decently documented disk image format I've found is qcow2. [0] Which is usually not the best tool for the job.

So very many of them are just header details + "only works with our tools".

[0] https://www.qemu.org/docs/master/interop/qcow2.html

https://docs.kernel.org/filesystems/ext4/index.html

A filesystem is not a disk image.

If it quaks like a disk image, it is a disk image

A filesystem is not a file.

(Yes, you can store a filesystem in a file - and that's a trivial sort of disk image, but one with some serious drawbacks like "you have to allocate all of the space up front". We can do better.)

Some of the most popular disk image formats are basically a sparse file abstraction for non-sparse files and nothing more. You have a bunch of blocks, a table mapping each block to its virtual location, and a couple convenience headers.

If those count as a disk image when you put a filesystem inside, then I say a normal file is also a disk image when you put a filesystem inside.

Especially because the sparse mapping is optional. For example, lots of VHDs are a raw file plus a 512 byte footer.

What?

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